Sifcon Concrete 5p343h

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CHAPTER - 1 INTRODUCTION 1.1 General Concrete technology has made tremendous strides in the past decade. Concrete is now no longer a material consisting of cement, aggregates, water and ixtures but it is an engineered material with several new constituents performing satisfactorily under different conditions. Concrete today can be tailor made for specific applications and contain different materials. The development of specifying a concrete according to its performance requirements rather than the constituents and ingredients has opened innumerable opportunities for producers and s to design concrete to suit to their specific requirements. One of the spectacular advances made in the field of Civil Engineering is the production of high performance materials. Development of modern civil engineering causes an urgent need to develop higher performance engineering materials possessing high strength, toughness, energy absorption and durability. Fiber reinforced concrete (FRC) is one of the conventional engineering materials used in several structural applications in order to enhance the structural resistance/performance under different loading combinations. It also increases speed of construction and may even eliminate the need for conventional reinforcement. High or ultrahigh strength concrete with very high compressive strength values remains basically a brittle material. The inclusion of adequate fibers improves tensile strength and provides ductility. Since the 1980’s, the design and construction of structural demand more and more high performance materials. High performance construction materials provide far greater strength, ductility, durability, and resistance to external elements

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than traditional construction materials, and can significantly increase the longevity of structures in the built environment and can also reduce maintenance costs for these structures considerably. These most significant high performance construction materials include high performance concrete, high performance steel, fiber reinforced cement composites, FRP composites, etc.

Slurry infiltrated fibrous concrete

(SIFCON) is one of the high performance material. As the fibre concentration is increased along with fibre aspect ratio (length/diameter), it becomes difficult to mix and place these materials. In practice it has been found that the amount of fibre must be kept fewer than 2% volume and aspect ratio must be kept under 100. This situation places bounds on the improvements in the engineering properties of concrete (flexural strength, flexural toughness index, impact resistance and fatigue resistance) that can be gained through the use of steel fibres. In 1978, Lankard began an investigation to incorporate larger amounts of steel fibres in steel fibre reinforced cement based composites. The result of this investigation led to the development of new cement composite called “Slurry Infiltrated Fibre Concrete (SIFCON)” in which steel fibres up to 20% by volume could be used.

1.2 About SIFCON 1.2.1 Introduction Initially steel fibers were mostly used as a substitute for secondary reinforcement or for crack control in less critical parts of the construction. Today steel fibers are widely used as the main and unique reinforcing for industrial floor slabs, shotcrete and prefabricated concrete products. They are also considered for structural purposes in reinforcement of slabs on piles, full replacement of the standard

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reinforcing cage for tunnel segments, concrete cellars, foundation slabs and shear reinforcement in prestressed elements. Slurry Infiltrated Fiber Concrete (SIFCON) is one of the recently developed construction material that can be considered as a special type of high performance fiber reinforced concrete (HPFRC) with higher fiber content. In 1979 a new material, slurry-infiltrated fiber concrete (SIFCON), was introduced by Dr. David Lankard of the Lankard Materials Laboratory (LML) in Columbus, Ohio. Dr. Lankard had done some pioneer work in the development of the material, as well as some applications using the material in the paving and metal fabrication industries. SIFCON possessed the characteristics of both high strength as well as ductility. SIFCON can be rightly thought of as pre- placed fibre concrete, analogous to pre- placed aggregate concrete. In FRC the fibres are mixed along with the other ingredients but the placement of steel fibres in a form or mould is the initial step in the preparation of SIFCON. Fibre placement can be accomplished by hand or through the use of commercial fibre dispersing units. Light external vibration is applied during the fibre placement operation. Once the fibres are in place, fine grained cement based slurry is poured on to the packed fibre bed with subsequent infiltration of the slurry added by external vibration. High range water reducing ixtures are used to provide suitable slurry viscosity while maintaining a low water cement ratio. Once the slurry infiltration is completed, the method of curing of SIFCON is the same as for any concrete material. The matrix fineness must be designed so as to properly infiltrate the fiber network formed in the mould. Otherwise large pores may form leading to substantial reduction in the mechanical properties. Additives such as high range ixtures such as super plasticizer are used for improving the flowing characteristics of SIFCON.

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1.2.2 Advantages In general, SIFCON is very ductile and particularly well suited for structures which require higher ductility. 

SIFCON possess excellent durability, energy absorption capacity, impact and abrasion resistance and toughness.

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Modulus of elasticity (E) values for SIFCON specimens is higher when compared with plain concrete.

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SIFCON exhibits high ductility.

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The balling problem of steel fibers with increase in fiber volume in SFRC can be resolved by SIFCON, because of its fiber alignment.

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Deflection for SIFCON will be very less compared to conventional concrete structural components.

Since properties like ductility, crack resistance and penetration and impact resistance are found to be very high for SIFCON when compared to other materials, SIFCON should be considered as an efficient alternative construction material only for those applications where concrete or conventional SFRC cannot perform as may be expected/required by the or in situations where such unique properties as high strength and ductility are required. SIFCON is best suited for application in the following areas: 

Pavement rehabilitation and precast concrete products

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Overlays, bridge decks and protective revetments

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Seismic and explosive-resistant structures

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Security concrete applications (safety vaults, strong rooms etc)

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Refractory applications (soak-pit covers, furnace lintels, saddle piers)

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Military applications such as anti-missile hangers, under-ground shelters

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Sea-protective works

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Primary nuclear containment shielding

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Aerospace launching platforms

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Repair, rehabilitation and strengthening of structures

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Rapid air-field repair work

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Concrete mega-structures like offshore and long-span structures, solar towers etc

1.3 Need of the present study SIFCON is similar to FRC in that it has discrete interlocking fibre that lends significant tensile properties to the composite. In SIFCON, the fibres are preplaced inside the forms and rich cement slurry is poured into the moulds. Its ability to resist cracking and spalling in many loading situations is far superior to conventional fiber reinforced concrete and to conventionally reinforced cement concrete. All the research in U.S.A and Europe is focused on SIFCON produced with high tensile strength steel fibres. However, for greater applications in India and other developing countries, it is essential to investigate the feasibility of producing different SIFCON structural elements with locally available low tensile strength steel wire fibres and understanding their behaviour. Even though, SIFCON is a recent construction material, it has found applications in the areas of pavements repairs, repair of bridge structures, safe vaults and defense structures due to its excellent energy absorption capacities.

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It is observed from the review that very little research is carried out to study the behavior of SIFCON slab elements using analytical methods. With this view, an analytical investigation has been carried out using FEM software in the present work to understand the flexural behaviour of SIFCON slab s. Experimental based testing has been widely used as a means to analyze individual elements and the effects of concrete strength under loading. The use of finite element analysis to study these SIFCON slab components will be quite interesting. Despite its long history, the finite element method continues to be the predominant strategy employed by engineers to conduct structural analysis. A reliable method is needed for analyzing structures made of SIFCON, a complex but rare ingredient in most of the structural components. As an effective alternative to expensive experimentation, this study has been conducted to evaluate the plausibility of finite element analysis of SIFCON slabs.

1.4 Objectives of the present Investigation The objective of present investigation is to investigate and evaluate the use of the finite element method for the analysis of solid SIFCON slab with and without opening at different positions with available material properties in flexure as such models are not available for SIFCON slabs. Accordingly, the specific objectives of the present work are listed below. 

To conduct a feasibility study of producing SIFCON slab elements with locally available low tensile strength steel wire fibres.

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To model Slabs with different edge conditions for 8%, 10% and 12% volume fraction of fibre using FEA in flexure under uniform distributed load.

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To evaluate and compare the strength and stiffness properties of FE modelled slab with that of experimental values.

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To the accuracy of the model with experimental values.

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Also to evaluate the total energy absorption capacity of SIFCON slabs modeled using FEA in flexure.

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To compare the load deflection response obtained from FE analysis with experimental values.

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To study the variation in the spread of normal stresses at the bottom surface of the SIFCON slabs by FEA.

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To model SIFCON slab with different type and size openings for different edge conditions in flexure under uniformly distributed load

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To validate the proposed FE solution by comparing the solid SIFCON slab results with experimental values available in literature.

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To analyse SIFCON slabs with openings of different sizes and locations using validated FE SIFCON models. Thus, it is proposed to study the response of slurry infiltrated fibre concrete

slabs using finite element analysis to understand their load-deflection response under pressure loading. A slurry infiltrated fibre concrete slab model will be developed using FEM and the results will be compared to experimental data in this project. Slabs with different edge conditions for 8%, 10% and 12% volume fraction of fibre will be analysed using FEM. NISA, a general purpose Finite Element Software, will be used for this purpose. Solid elements will be used to develop the slab model and the accuracy of the model will be verified with experimental values. Concrete structural components exist in buildings and bridges in different forms. Understanding the

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response of these components during loading is crucial to the construction of an efficient and safe structure.

Different methods have been utilized to study the

response of structural components. Experimental based testing has been widely used as a means to analyze individual elements and the effects of concrete strength under loading. While this is a method that produces real life response, it is extremely time consuming and quite costly. The use of finite element analysis to study the structural components can be quite effective. In recent years, the use of finite element analysis has increased due to progressing knowledge and capabilities of computer software and hardware. It has now become the choice method to analyze concrete structural components. The use of computer software to model these elements is much faster, and extremely cost effective. Thus use of FEA has been the preferred method to study the behavior of concrete. The results will be analyzed and useful conclusions will be drawn. It is felt that this will lead to a chain of development in the field of SIFCON and thus leads to greater applications of this material in this country.

1.5 ORGANIZATION OF THE THESIS The presentation of the investigation carried out to achieve the specific objectives mentioned in the previous section is planned in the following manner:

Chapter 1 This chapter covers the general background to the problem, motivation for the present work, objectives of the present study and organization of the thesis.

Chapter 2 This chapter deals with the comprehensive literature review in the area of the present work and critical review of the literature. It covers in detail the analytical

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solution for slabs using FEA. Based on this, the scope and objective of the present study has been derived.

Chapter 3 This chapter deals in detail with the finite element techniques and constitutive models that have been used in the analysis. The details of modeling and validation of finite element programme used are presented in this chapter.

Chapter 4 This chapter presents the details of tests conducted on basic raw materials like cement, fine aggregate, water and steel fibres used in the present investigation. The experiments have been conducted as per the specifications of relevant I.S codes for deriving properties of SIFCON.

Chapter 5 This chapter presents the FE analysis of solid two way SIFCON slabs without openings for different edge conditions and with 8%, 10% and 12% volume fraction of fibre.

This chapter presents a complete analysis viz., load-deflection response,

stiffness, energy absorption and normal stresses at the bottom face of SIFCON slabs for evaluating the response of SIFCON slabs under pressure loading.

Chapter 6 Chapter 6 deals with the details of the SIFCON slab flexure model using FEA with different openings at center and deriving the load deflection response. The details of models of slabs with different edge conditions for 8%, 10% and 12% volume fraction of fibre have been reported in this chapter.

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Chapter 7 This module deals with the details of the SIFCON slab flexure model using FEA with different openings at corner subjected to pressure loading and derivation of the load deflection response. The details of models developed for slabs with different edge conditions for evaluating load deflection response and their behaviour with different volume percentages of fibre (i.e. 8%, 10% and 12%) have been reported.

Chapter 8 This chapter deals with the details of the SIFCON slab flexure model using FEA with different openings at different position in slab subjected to pressure loading to evaluate the load deflection response. The details of models developed for slabs with different edge conditions for evaluating load deflection response and their behaviour with different volume percentages of fibre (i.e. 8%, 10% and 12%) have been reported.

Chapter 9 This chapter outlines the overall conclusions and inferences drawn from this investigation along with the suggestions for further investigation. A comprehensive bibliographical list is provided at the end of the thesis with a view to help present and future investigators working in the related areas.